Process of treating fatty acids



Patented Aug. 29, 1950 PROCESS OF TREATING FATTY ACIDS Latimer D. Myers,Cincinnati, Ohio, assignor to Emery Industries, Inc., Cincinnati, Ohio,a corporation of Ohio No Drawing. Application March 28, 1945, Serial No.585,387

7 Claims. 1

This invention relates to a process of purifying fatty acids. It isdirected particularly to a method for removing unsaponifiable materialsfrom commercial fatty acids in order that they will be less contaminatedwith foreign substances and therefore more valuable. This application isa continuation in part of my copending application, Serial No. 420,106,filed November 22, 1941, now abandoned.

The fats and greases from which commercial fatty acids are obtained orproduced contain amounts of unsaponifiable material and the nature ofthis contamination varies sometimes in accordance with the sources fromwhich the fatty acids are produced and sometimesfrom batch to batch offatty acids derived from a given source. For example, the variation inthe unsaponifiable content of fatty acids is illustrated in the tablewhich follows:

Per cent Prime tallow 1 Diamond S tallow 1.25 Yellow grease stearine1.25 Brown or horse grease 1. 6 Bone grease 1.5 Extracted grease 2.5Garbage grease 4-9 Among the compounds which may be present are thsterols, such as cholesterol and phytosterol, higher alcohols andhydrocarbons either naturally occurring or present as contaminants.Greases produced. in extraction processes often contain high boilingconstituents derived from the solvent with which the greases wereextracted from the animal tissue.

In the manufacture of stearic and oleic acids from greases of the typeillustrated in the example the unsaponifiable content is found mainly inthe oleic acid fraction. Its presence is undesirable inasmuch as it isan inert substance which is valueless for use in soap making, one of thechief purposes for which oleic acid is employed, but also because ittends to cause cloudy soap solutions when present in too greatquantities.

Purchasers of commercial oleic acid specify limits which theunsaponifiable content may not exceed and the price of the commercialacids fluctuates in accordance with the percentage of contamination;oleic acid with a low unsaponifiable content often commands a premium inprice. These same marketing rules are observed with respect to thenatural fats from which the fatty acids are derived and it is thereforedistinctly desirable to be able to produce an oleic acid which containsas little in amount as unsapom'fiable material as possible from a fatwhich may contain a relatively large amount.

The principal objective therefore has been to provide a method by whichthe unsaponifiable content of fatty acids may be reduced in the processof fatty acid manufacture.

Fatty acids are generally manufactured from dark colored raw materials.Light colored fatty acids are produced by distilling the fatty acidsafter they are split off from the fatty glycerides. The distillation iscommonly carried out in two stages, the first stage being so conductedthat a residue is obtained containing approximately 15% of free fattyacid together with neutral fat and a considerable proportion of theunsaponifiable material originally present in the stock. This residuemay either be split further to decompose additional quantities ofneutral fat and,

to leave in the still tar or fatty acid pitch of an acceptableconsistency and melting point.

As the major portion of the unsaponifiable appears to have a slightlyhigher boiling range than the fatty acids which are present, aconsiderable portion of the unsaponifiable products remains in thepitch. However, the last portion of the distillate may contain from 20%toas high as 40% of unsaponifiable material, the remainder being fattyacids.

This invention resides in the discovery that the fatty acids andunsaponifiable materials possess differential solubilities in certainsolvents which makes it possible to obtain two fractions, one consistingprincipally of unsaponifiable material While the other is relatively lowin unsaponifiable content. More specifically, the invention resides inthe method which comprises admixing the fatty acids containingunsaponifiable material with a solvent in which the fatty acids are moresoluble than the unsaponifiable material and in such amount that theunsaponifiable material becomes immiscible with the solvent.

containing the fatty acids, then separating the two components from oneanother and finally removing the solvent from the fatty acid. Anysolvent taken from the solution upon separation of the unsaponifiablematerials therefrom may also be recovered by distillation.

Solvents which are suitable for the operation of this process are thosewhich may be characterized as very good solvents for fatty acids, butrather poor solvents for hydrocarbons. Typical solvents are lowmolecular weight alcohols, acids or ketones containing not more thanthree carbon atoms. Methyl alcohol has been found to be a verysatisfactory solvent; acetic acid is also suitable; acetone can be usedbut is not a satisfactory as methyl alcohol due'to its greatersolubility for hydrocarbon oils. Briefly, then, in the process of thepresent invention the fatty acid containing unsaponifiable material isadmixed with the solvent ofthe type described and the mixture is thenpermitted to settle. Two layers are formed, an upper layer containingfatty acids free or substantially free of unsaponifiable contaminantsand a lower layer consisting of some of the solventand a largepercentage if not all of the unsaponifiable material originallycontained in admixture with the fatty acids. These two layers areseparated and the solvent content of the lower layer sub sequently-mayberemoved as by evaporation; e purity of fatty acids obtained-in thisman her, so far as unsaponifiable contaminantsfare concerned fexceedsthe purity of-fa tty acids obtainecreveh by the mjost'carefuldistillation'proc'edure" and the process, therefore; is oneenablingfatty acids off greater value to be obtained at low cost} a-Considering methanol as a typical and entirely suitable solvent, it hasbeen found that certain conditions should Ice observed in order toobtain the ir'i axirnum degree of separation consistent: with economicaloperation.

The coiicentration "of the fatty acids in the alcohol sci-muons "ofgreat importance. The solubilityof the unsaponifiable material in thesolution of fatty acids in methanol is'prop orti'on'al to theconcentration of the fatty acids, that is a concentrated'solution offatty acids in 'methahol hassolvent characteristics an.- proaching thoseof fatty acids in'wliich unsaponifiable 'material issoluble in'allproportions "at ordinary temperatures; For this reason a lowconcentration-'of'fatty'acid inalcohol is desirable; Usually theconcentration er fatty acid should notf-exceedapproximately by weight ofthesolven t -The temperature at which the separation is effected alsoaffects the results obtainedi The temperature must be kept highenough topre'-' vent:"crystallization from solution of the solid fatty acids, 1.e., about 31) degrees C'j With an increase' in temperature the amount ofthe high unsaponifiable content layer decreases but its actualunsaponifiable content increases; that is, atia higher temperature lessfatty acids are carried down by the unsaponifiable layer. However; atthe same time the unsapon'ifiable con tent. of the alcohol fattyacid-solutionincreases toithe same content. In' other words;increasedtemperatures increase the solubility of the fatty acids thesolvent resulting in a lower loss of fatty'acids; but also increases thes'olubilityof unsaponifiable in the alcohol layer. In general,temperatures of from 30 to 45 degrees 0. give the most satisfactoryresults point of yield and quality.

Decreasing the strength of the methanoldecreases the content of theunsaponifiable material in the methanol layer but results in excessivelyhigh losses of fatty acids in the unsaponifiable layer. For this reason.85 to 90%' meth-' anol is recommended. The effect of "variationinsolvent characteristics with alcoholic concenf'rom the I stand-'tration permits the operation of a recycling two stage process whichenables higher yields of lower unsaponifiable material to be obtainedthan can be economically attained by a single stage process. Thus, thefirst extraction may be carried out with 90% methanol which will yield afairly low unsaponifiable product; addition of waterto the alcoholicsolution thus obtained to reduce the'alcoh'olic strength to will effecta further separation of unsaponifiable but the quantity ofunsaponifiable layer will not be great enough to dissolve anyconsiderable quantity of fatty acids.

The'separation is conveniently carried out as a continuous process bymixing the distillate containing unsaponifiable material and the solventsuitable by a centrifugal pump which also serves to move the resultingsolution to a settling tank. Separation into two layers occursveryquick'ly and a tank of sufiicient size to provide 1Q minutessettling is ample. The upper alcoholic solution preferably is drawn 'oifcontinuously and'fed tofa'n evaporator the lower layer conta iningunsaponifiable material may be drawnjoif either byhand or by automaticfloat control continuously or intermittently and thereafter stored andevaporated periodically to recover the: solvent it contains.

The following examples illustrate the method of carrying out, theproposed process.

Er m

5 parts of tar still distillate containing 17.5% ofnns aponifiablematerial is mixed'with'ilfi parts of- 9tl%f weight methyl alcohol andallowed to stand atZ'Z- degrees C. The lower unsapo'nifiable layeramounts to 16.1% of the fatty acid takenand contains 22% of fatty acid,the remainder beingunsaponifiablewith'a few percent of neutral fat. Thealcohol solution is evaporated yielding 83.9% of fatty acid containing7.4%; unsaponifiable or. a. reduction of 10.1%, in.

xam e 3 Using ei am -unsapdn fia le. nt nt ma r rialas inExamplehbuttreating l5 par tswith amounts to 43.2% containing 38.5% freefatty acid, and the fatty acids recovered from the alcoholic solutiona'mgunredm 56.8% containing '7.88% unsaponifiablef. The unsapcnifiablereduction amounts to20.6.%. but the fatty acid loss amounts] to f16.'6%This "method which is coo nomical'from the standpoint of quantity ofalcoh'o'lwhi'ch must be distilled can be recommended only when fattyacids of low value are processed.

' Q I Example 4 5' parts of tar stilldistillate containing 20% ofunsaponifiable material'were'treated with 95 parts ofby weight methanolat 50 degrees C.- The lower layer amountedto 2 .37% contain-- ing 26.5%free fatty acidl' The remaininguppcr layer contained 5.6%offunsaponifi'ab-le or about 22.5% less than would be obtained by acorresponding treatment with 90% methanol.

Example 5 Tar still distillate containing 20% unsaponifiable was treatedin 10.8% concentration with 90% by weightmethanol. 14% of lower layercontaining 24% free fatty acid was obtained, a sample of the upper layershowed 10.5% unsaponifiable content. Water was then added to the upperlayer until the alcohol strength was reduced to 82%. A second lowerlayer amounting to 34.8% containing 65% of free fatty acid separated.The solution remaining yielded fatty acids containing 4.5%unsaponifiable. The second residue, being high in free fatty acidcontent, may be retreated with 90% methanol by blending with the feed.In this case a corresponding increase in amount and unsaponifiablecontent of the first residue results. The alcohol from the secondoperation is rectified during distillation to increase its concentrationfor reuse in the first operation.

From these examples it will be apparent that the process disclosed doesnot fractionate the fatty acids and the unsaponifiable material sharplyand that when the unsaponifiable content of the solution is below 7%unsaponifiable to 93% fatty acids, a substantial amount of fatty acidsdoes not go into solution but remains with the unsaponifiable material.The process therefore is not suitable for commercial use under a greatvariety of conditions in a fatty acid plant.

The invention is primarily intended and adapted for use when fatty acidshaving an unsaponifiable content above 10% are to be purified. Such highunsaponifiable contents do not occur in natural fats or commonly ingarbage grease. Rather such high unsaponifiable contents result from theaccumulation of smaller amounts of unsaponiiiable material in thestarting products, for instance, the still residues previouslydescribed. In the case of still residues, the high unsaponifiablecontent is the result of repeated distillations by which free fatty acidis removed from the stock.

The process is not particularly suitable for treating still residues andobtaining fatty acids which by themselves are of commercial valuebecause if the process is operated to remove a substantial proportion ofthe fatty acids in the still residues then, as explained, its content ofunsaponifiable is too high for most commercial purposes. Fatty acidsobtained must usually be mixed with fatty acids of greater purity toproduce a product of sufficiently low unsaponifiable content.

On this account I prefer to use the process of this invention incombination with the process of separating fatty acids by solventseparation. This process is described and claimed in Patent No.2,293,676, issued August 18, 1942, Method of Separating Fatty Acids.According to the disclosure of this patent the mixed fatty acids aredissolved in a solvent, such as strong methyl alcohol, the strength ofthe solution of the fatty acids in the alcohol being -30% by weight;then the temperature is lowered to precipitate the solid acid fractionsafter which they are separated from the solution by filtration. When theprocesses are used com'ointly the solvent is first used to extract freefatty acids from the still stock, after which additional fatty acids areadded to provide a total concentration of fatty acids in alcohol ofabout The solution .is then chilled to precipitate the solid fatty acidswhich are removed by filtration. In this way, -the unsaponifiablecontent of the final product is. kept within commercial limits, yetwastage of the fatty acids in the still residues is avoided. 1

Having described my invention, I claim:

1. The method of purifying fatty acid stocks, the unsaponifiable contentof which is greater than 10 said method comprising treating saidmaterial with a solvent of the class consisting of lower molecularweight alcohols, acids and ketones, containing not more than threecarbon atoms, the concentration of fatty acids in the solvent solutionnot exceeding substantially 10%, then adding fatty acids of lowerunsaponifiable content to said solution to increase the concentration offatt acids in the solution to substantially 30%, then chilling saidsolution to precipitate the solid fatty acids in it and removing themfrom said solution by filtration.

2. The method of treating tar still distillate, which comprises admixingthe tar still distillate with about twenty parts by weight ofapproximately methyl alcohol, settling the unsaponifiable material fromthe solution while the solution is held at a temperature of about 30 to45 C., separating the solvent solution of tar still distillate from thesettled unsaponifiable material and separating the methyl alcohol fromthe fatty acids.

3. A process of preparing purified fatty acids which comprises admixingfatty acid tar still distillate with methyl alcohol to obtain a solutionnot exceeding substantially 10% concentration and separating theunsaponifiable material from the solution while the solution is held ata temperature of about 30 to 45 C. and thereby extracting free fattyacids from the still stock, and subsequently adding fatty acid stockhaving a lower unsaponifiable content than the still stock to theextract to increase the concentration of fatty acid therein tosubstantially 30% and subsequently chilling the solution to precipitatesolid fatty acids therein, and removing said precipitated solid fattyacid.

4. A method of recovering fatty acid values from tar still distillate,which method comprises admixing one part of distillate to about twentyparts by weight of approximately 90% methyl alcohol and therebyextracting free fatty acids from the still stock and subsequently addingto the extract fatty acids of a lower unsaponifiable content than thetar still distillate to increase the fatty acid concentration thereof toapproximately 30 then chilling the extract of the increased fatty acidconcentration to precipitate fatty acids therein and removing said fattyacids from said solution by filtration.

5. A method of processing fatty acids comprising dissolving 5 to 10parts fatty acids of high unsaponifiable content in from 90 to parts offrom 85 to 95% methanol at a temperature of from 30 to 45 0., allowingthe mixture to settle to effect a separation of unsaponifiable material,withdrawing the alcohol solution of fatty acids, adding additionalquantities of fatty acids to said solution and proceeding with theseparation of the solid and liquid fatty acids.

6. The method of obtaining from tar still distillate which has anunsaponifiable content of above 10%, a fatty acid product having alesser unsaponifiable content, said method comprising treating the tarstill distillate with a solvent of the class consisting of lowermolecular weight assets- 6 *tion from the residue which does not enterinto the solution and separating the solvent from the fatty acidswhichar'e dissolved in it.

7. The method of obtaining commercial solid and liquid fatty acidfractions utilizing as an ingredient tar still distillate having an*un'sap'onifiable-content of greater than 10%, said method comprisingtreating the tar still 'distillate with a solvent of the-classconsisting of lower molecular Weight alcohols, acidsandlaetonescontaining not more than three carbon atoms to 'provide asolution of fatty acid in solvent in which the concentration of fattyacids is "less than 10% by Weight, separating the solution from "the"residue whichdoes not enter into solution, addingfatty acids to thesolution to increase the fatty acid concentration of the solution tosubstantially 30% and separating the solid and liquid fatty acids insolution from each \other.

LATIMER D. MYERS.

REFERENCES CITED Thepfollowing references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,113,960 G-rote Apr. 12, 1938$298,501 Meyers et a1 Oct. 13,1942 2,381,420 'Balch Aug. 7, 1945 OTHERREFERENCES Ubbel'ohde: Handbuch der Chemie und "-Iechnol'og'ie der Oleund Fette, v01. '3, page 209, Leipzig, '1910.

6. THE METHOD OF OBTAINING FROM TAR STILL DISTILLATE WHICH HAS ANUNSAPONIFIABLE CONTENT OF ABOVE 10%, A FATTY ACID PRODUCT HAVING ALESSER UNSAPONIFIABLE CONTENT, SAID METHOD COMPRISING TREATING THE TARSTILL DISTILLATE WITH A SOLVENT OF THE CLASS CONSISTING OF LOWERMOLEUCLAR WEIGHT ALCOHOLS, ACIDS AND KETONES CONTAINING NOT MORE THANTHREE CARBON ATOMS TO PROVIDE A SOLUTION IN WHICH THE CONCENTRATION OFTHE FATTY ACIDS IS LESS THAN 10% BY WEIGHT, SEPARATING THE SOLUTION FROMTHE RESIDUE WHICH DOES NOT ENTER INTO THE SOLUTION AND SEPARATING THESOLVENT FROM THE FATTY ACIDS WHICH ARE DISSOLVED IN IT.